Feature/37 terraform created files in archive

[taylorludwig]

Fixes #37

Uses an approach similar to described in hashicorp/terraform-provider-archive#11

Adds a new optional input var source_dependent_files that can take a list of local_file resources.

This then forces the archive to not be created until all other terraform created files are in the source directory. Prior to this the archive would be created before any terraform created local_files existed.

With the extra null_resource and null_data_source workaround it allows terraform to converge (terraform plan/apply wont show changes unless there are actual file changes in source_directory or terraform created local_files). The comment above describes more why the workaround is needed.

A new example and test is created to demonstrate this by simply having the function return back the value of the random created terraform file.

Once this is in we can go back and properly fix terraform-google-modules/terraform-google-slo#7

[ocervell]

@taylorludwig thank you so much for this and creating a PR in terraform-google-slo too ! Will test this out and review shortly.

[aaron-lane]

Thanks @taylorludwig!

[ocervell]

@taylorludwig thanks so much for this